MANILA, Philippines (AP) — The Philippine government summoned China’s top envoy in Manila on Tuesday to protest what it said was the firing of a water cannon by a Chinese government vessel to drive away Filipino fishermen in a disputed shoal in the South China Sea, the latest barb in their territorial rift.

Department of Foreign Affairs spokesman Raul Hernandez said a diplomatic protest was handed to Beijing’s charge d’affairs over the Jan. 27 incident at Scarborough Shoal, a rich fishing ground claimed by China and the Philippines.

The shoal came under Chinese control after Philippine vessels backed off from a tense standoff with Chinese ships in the area in 2012.

Chinese coast guard and surveillance ships have since guarded the shoal, chasing Filipino fishermen away if they venture close. The Philippines has not deployed its ships to try to take back control of Scarborough but asked an international tribunal last year to declare China’s seizure of the shoal and seven other South China Sea reefs illegal.

A Chinese coast guard vessel with bow No. 3063 used its water cannon for several minutes and sounded its horn to drive away two Filipino fishing boats near Scarborough, Hernandez told a news conference, adding it was the first time Chinese authorities had carried out such a hostile act against Filipino fishermen.

“Bajo de Masinloc is an integral part of the Philippines and over which the Philippines exercises sovereignty, sovereign rights and jurisdiction,” Hernandez said, using the Filipino name for the vast shoal area.

Filipino fish trader Macario Forones said Chinese coast guard personnel used waste water laden with oil while blowing the horn and yelling “Go away, go away” at his fishermen. One or two other Philippine fishing boats were hit by the waste water, he said.

“The water smelled of oil and smeared the side of my fishing boat,” Forones told The Associated Press by telephone. “But my fishermen did not really leave the area. We’ve spent so much money to travel there and they basically ignored the Chinese.”

Nine other instances of harassment were committed by Chinese government vessels on Filipino fishermen last year, including when Filipinos were prevented from taking shelter at the shoal during stormy weather, Hernandez said.

President Benigno Aquino III said his government wanted an explanation from Beijing.

Chinese Embassy officials did not immediately react to the Philippine protest.

Hernandez said the Philippine government would take steps to protect its fishermen, but he did not specify how.

Military chief of staff Gen. Emmanuel Bautista told reporters Monday that Philippine forces adhere to a no-confrontation policy in the disputed areas but would defend the country and its people if they are threatened.

China, the Philippines and four other governments have been disputing ownership of resource-rich South China Sea territories for years. Many fear the disputes, which have sparked tensions and strained ties between the rival claimants, could set off an armed conflict.